Piston



Sept. 19, 1933. I L, MOORE 1,927,611

PISTON Filed June 21, 1930 ausm Patented Sept. 19, 1933 UNITED STATES PATENT OFF! PISTON George L. Moore, Cleveland, Ohio, asslgnor, by

mesne assignments, Company, Trustee, 01 tion of Ohio to The Cleveland Trust eveland, Ohio, a. corpora- Application June 21, 1930. Serial No. 462,761

8 Claims.

be maintained between the skirt and the'cylinder wall throughout the range of operating temperatures. It has been found, however, in some instances, that the rapidly fluctuating pressures to which the thrust faces of the piston are subjected and the consequent repeated flexing of the portions of the skirts immediately adjacent the splits tend to give rise to fatigue of the metal of these portions, resulting in a permanent set thereof inwardly of the original outline of the skirt. Such changes in shape permit piston slapping and oil pumping and, in time, largely defeat 23 the purpose of the split skirt. Accordingly, the

' primary object of this invention is to provide a split skirt piston which will not be subject to collapse or distortion, but which will be sufliciently flexible to compensate for thermal expansion to permit the maintainance of a close clearance throughout the range of operating temperatures.

Another object is to construct the thrust face of the piston which is to resist the thrust of the compression stroke in an internal combustion en- 3 gine in such a manner as to compensate for the circumferential expansion of the entire skirt.

A further object is to provide a piston with intersecting slots on one thrust face near the top of the skirt to permit this portion of the skirt of the piston to flex and yield to compensate for when cold without danger of scoring or undue friction when hot.

A further object is to provide a piston possessing to a high degree the advantages and to a lesser extent the disadvantages of both the full trunk type piston and the flexible Skirt piston,

and one which may be economically manufactured in permanent molds.

Other objects and advantages more or less ancillary to the foregoing and the manner in which the various objects are realized will appear in the following description.

In the accompanying drawing, which in conjunction with the description discloses a preferred embodiment of this invention:

Fig. 1 is an elevation of one form of the improved piston.

Fig. 2 is a section taken on the line 2-2 of Fig. 1 looking in the direction of the arrows.

' Fig. 3 is a section taken on the line 3 3 of Fig. 2, looking in the direction of the arrows.

and a cylinder taken on the plane indicated by the line 44 of Figure 1 looking in the direction of the arrows, and showing greatly exaggerated the clearances between the walls of the piston and the cylinder at different points.

' Referring to the drawing, the piston consists of a head 5 having a depending annular flange 6 provided wih machined grooves 7 to receive the usual piston packing rings. A skirt 8 is integral with the flange 6 and is formed with integral oppositely disposed bosses 9 having cored out openings 10 to receive the usual piston pin which serves to articulate the piston to a connecting rod of an engine. A continuous strengthening rib 11 extends across the inner surfaces of the head 5 and merges into the bosses 9.- Substantially triangular webs 12 join the lower sides of the bosses 9 with the lower portion of the skirt 8.

The surface 13 of the skirt 8 extending between the bosses 9 on one side constitutes the maximum thrust face; that is, the face which receives the lateral thrust of the power stroke in the internal combustion engine. The opposite surface 14 constitutes the minimum thrust face, adapted to receive the thrust of the compression stroke. The minimum thrust face 14 is provided with a horizontal split 15 separating the same from the flange 6 of the head and extending through about '75 or 85 degrees on each side of the center line of this face. A substantially vertical split 16 extends downwardly from the horizontal split 15 approximately two-thirds of the length of the skirt at or near the center line of the minimum thrust face 14. The remainder of the skirt is left unslotted, so that the piston pin bosses 9, the maximum thrust face 13 and the head 5 constitute a continuous unitary structure similar to a full trunk type piston. The bottom of the mini- Figure 4 is a sectional viewthrough the piston mum thrust face 14, through about a third of its height, is also solid and integral with the piston pin bosses 9.

In finishing the piston the flange 6 of the head is ground to a diameter sufiiciently small to prevent contact of the same with the wall of the cylinder in which the piston is to operate under any conditions of expansion. The piston rings which are positioned in the grooves 8 bear on the cylinder walland seal the combustion space. The

skirt of the piston is preferably ground by means of a cam grinder so that the maximum thrust face 13 is substantially circular in cross section and the minimum thrust face 14 has an oval shape with its major axis on a line through the centers of the thrust faces. This cross-sectional contour is preferably uniform throughout the height of the skirt. In order to prevent contact between the piston pin bosses 9 and the cylinder wall, relieved areas 17 are formed about the bosses.

The skirt is finished to such dimensions that it may be fitted to a cylinder when cold with a close clearance on a line extending through the centers of the thrust faces, the clearance being substantially uniform about the maximum thrust face and increasing from the center line of the minimum thrust face toward the piston pin bosses. When the engine is operating the lateral thrust of the power stroke is resisted by the solid cylindricalmaximum thrust face 13'without flexure or distortion of the skirt in any manner. The relation of the walls of the piston to the cylinder walls when the piston is cold is shown in exaggerated form in Figure 4. As shown in this figure the maximum thrust face 13 is uniformly spaced from the cylinder wall a relatively small amount. preferably the thickness of the oil film or a sufficiently small amount to prevent the piston slap. The center of the minimum thrust face 14' is in corresponding clearance relation with the cylinder wall. From the center the clearance of the minimum thrustface 14 increases resulting from the, oval shape of this face, in both directions toward the wrist pin bosses. The oval contour of the minimum thrust face 13 merges into the circular sectional contour of the maximum thrust face 13 through the areas of the lower portion of the skirt disposed below the wrist, pin

bosses which may be arranged in the usual circular sectional formwith suflicient clearance to accommodate the expansion parallel to the wrist pin axis as previously explained.

The extremely high temperatures existing in the combustion space above the head of the piston during each explosion'heat the piston up as the engine continues to operate. The heat absorbed by the head of the piston flows downwardly into the skirt and is absorbed by the walls of the cylinder, which are ordinarily cooled by circulating water, air or other medium. As a result, the upper portion of the piston skirt is maintained at the highest temperature, the, lower portion remaining relatively cool. The absorption of the heat by the cylinder walls is assisted in the present instance by the continuous structure of the maximum thrust face and the piston head, permitting an unrestricted flow of the heat, and the full circular contour of the maximum thrust face, causing intimate engagement of the same throughout its area with the =cylinder-wall a .nd

the split 15, does not receive as much heat as the face 13.

The heating of the upper part of the skirt causes expansion thereof which is primarily absorbed by the split 16, the edges of the split-approaching each other slightly as the skirt expands circumferentially. The oval contour of the face 14 also approaches a circular contour, a portion of the expansion being absorbed by such movement. Since the lower portion of the skirt below the end of the split 16 does not reach as high a temperature as the upper portion, the entire expansion thereof is amply compensated by the approach of the ovaloutline of the face 14 toward a circular outline.

If desired, the oval contour of the face 14 may be obtained by pressing an oval plug into the bottom of the skirt with its major axis parallel to the axis of the piston pin bosses and then grinding the skirt round. When the plug is removed the minimum thrust face 14 and the bottom portion of the skirt spring to an oval shape, the upper portion of thelmaximum thrust face 13 remaining substantially circular due to the absence of splits which would permit the plug to distort the same. the upper portion of the skirt, as explained When formed in this way.

above, has substantially the contour illustrated bottom of the skirt'below the lower end of the vertical slot 16 difiers from the contour illustrated in Figure 4 in that the complete band is .a substantially symmetrical oval with the major 'in Figure 4. The continuous band left at the construed as restrictive or limiting, and it is to be further understood that various modifications and rearrangements of parts may be resorted to without departing from the scope of the inven? tion as-claimed herein.

I claim: 1. A piston including a head, piston pin bosses, and a skirt, said skirt including opposed thrust faces, one of said thrust faces having a substan tially circular sectional contour, and the other ofsaid thrust faces having a substantially vertical slot therein terminating short of the bottom of the skirt, said last named thrust face, including the portion between the bottom of the slot and the bottom of the skirt, having an oval sectional contour.

2. A piston including a head, piston pin bosses, and a skirt, said skirt including opposed thrust faces, one of said thrust faces having a substantially circular sectional contour, and the other of said thrust faces having a substantially vertical slot therein terminating short of the bottom of the skirt, said last named thrust face, in-

cluding 'the portion between the bottom of the slot and the bottom of the skirt, having a substantially elliptical'sectional contour, with its major axis at right angles to the axis of the piston pin bosses. p

pin openings and a substantially vertical slot formed on one side between the wrist pin open-j ings and terminating above the lower edge of the skirt, said piston being formed with a horizontal slot intersecting said vertical slot and partially separating the upper'edge of said skirt from the head, the ends of said horizontal slot being spaced from a vertical plane through the wrist pin axis, and said skirt having the remainder of its upper edge integrally joined to the lower edge of said ring flange, the lower portion of said skirt below .the end of the substantially vertical slot being circumferentially continuous and being formed out of round to yield when subjected to pressure on a line perpendicular to the wrist pin axis to prevent the same from binding in a cylinder during expansion of the piston.

e. A piston comprising a head having a depending'cylindrical ring flange, a skirt having wrist pin bosses formed therein and having a full exterior surface circumferentially continuous throughout except for oppositely disposed wrist pin openings and a substantially vertical slot formed on one side between the wrist pin openings and terminating above the lower edge of the skirt, said piston being formed with a horizontal slot intersecting said vertical slot and partially separating the upper edge of said skirt from the head, the ends of said horizontal slot being spaced from a vertical plane through the wrist pin axis, and said skirt having the remainder of its upper edge integrally joined to the lower edge of said ring flange, the lower portion of said skirt below the end of the substantially vertical slot being circumferentially continuous and having an oval portion to absorb expansion of the lower portion of the skirt.

5. A piston comprising a head having a depending cylindrical ring flange, a skirt having wrist pin bosses formed therein and having a full exterior surface circumferentially continuous throughout except for oppositely disposed wrist pin openings and a substantially vertical slot formed on one side between the wrist pin openings and terminating above the lower edge of the skirt, said piston being formed with a horizontal slot intersecting said vertical slot and partially separating the upper edge of said skirt from the head, the ends of said horizontal slot being spaced from a vertical plane through the wrist pin axis, and said skirt having the remainder. of its upper edge integrally joined to the lower edge of said ring flange, the lower portion of said skirt on the side of the skirt having the substantially vertical slot therein and below the end of said slot having a semi-ovate sectional contour with the major axis of the oval perpendicular to the wrist pin axis.

6. A piston comprising a head having a depending ring flange and a skirt having wrist pinbosses formed therein, the upper edge of the skirt being separated from the head on one side by a substantially horizontal slot, and the remainder of the upper edge of said skirt being continuously integral with said ring flange, said skirt being formed with a substantially vertical slot intersecting said horizontal slot and extending toward but terminating short of the open end of the skirt,

land being otherwise unslotted, the portion of the iiskirt below the lower end of said substantially vertical slot being circumferentially continuous, said skirt being formed throughout its height with a smaller diameter in the vertical plane through the wrist pin axis than at right angles thereto, to provide clearance at the ends of the wrist pin bosses and also to permit deformation of'said circumferentially continuous lower portion of the skirt.

'1. An internal combustion engine piston composed of aluminum alloy comprising integral head and skirt portions, the skirt having wrist pin bosses formed therein, an unslotted bearing portion on one side of the skirt between the wrist pin bosses integrally united with the head, a bearing portion on the opposite side of the skirt including bendable wings formed by the intersection of a circumferentially extending slot separating the head from the skirt and a longitudinally extending slot extending from the circumferentially extending slot toward but stopping short of the open end of the skirt, the skirt being formed at its open end beyond the ends of said longitudi nally extending slot with a circumferentially con-= tinuous ring portion having its exterior surface formed out of round to permit distortion thereof to compensate for thermal expansion, and said skirt being relieved on its exterior surface in the region of the wrist pin bosses.

8. A one-piece aluminum alloy piston designed to operate in an internal combustion engine cylinder, comprising a head having a depending ring flange, a skirt having wrist therein and having opposed thrust faces, the upper edge of one of said thrust faces and the upper edge of the portions of said skirt above said wrist pin bosses being integrally united with said ring flange, said one thrust face being continuous and unslotted, the other of said thrust faces being separated at its upper edge from said ring flange by a horizontal slot and being formed with a substantially vertical slot intersecting said horizontal slot substantially at its center and extending toward but terminating short of the open. end of said skirt, and being otherwise unslotted, whereby the upper portion of said last mentioned thrust face is formed with a pair of leaves integrally connected with the remainder of said skirt at bending zones extending along the lines connecting the lower end of said vertical slot with the opposite ends of said horizontal slot and running spirally along the surface of said skirt to resist flexing of said leaves under lateral thrust against the cylinder wall, and the portion of said skirt below the end of said vertical slot being circumferentially continuous and being out of round with a greater diameter perpendicular to the wrist pin axis than parallel therewith to prevent binding of said portion in the cylinder.

, GEORGE L. MOORE. 

